The present invention relates to a control device for an electric machine, a corresponding method and a corresponding motor controller.
A multiplicity of electric motors are used today in modern technical applications. For example, modern motor vehicles, e.g. hybrid vehicles or electric vehicles, can be operated by an electric motor. Electric motors can, however, also be installed, e.g., in industrial mechatronic systems.
In order to efficiently control such electric motors, it is necessary to very precisely detect the rotor position thereof. In synchronous motors, this can be carried out by inductive position transmitters. Such inductive position transmitters generate both a sine track and a cosine track, from which the rotor position of the respective electric motor can be calculated by means of an arc tangent function.
The angular value calculated by means of the arc tangent function can, however, be distorted if the angular position between the sinus track emitted by the sensor and the cosine track emitted by the sensor is not exactly 90°. In FIG. 6, a diagram is depicted which shows the angular error between the calculated and the actual angle if the angular position between the sine track and the cosine track of the sensor is not exactly 90°.
Such a distortion of the angular value negatively affects the transformation from the coordinate system fixed to the rotor into the coordinate system fixed to the stator, whereby the current indicator in the motor controller of the electric motor is set incorrectly.
In order to prevent this distortion of the angular value, an angle which is separate in each case for the sinus track and the cosine track can be calculated by means of an arc sine function or respectively an arc cosine function. The difference between the two calculated angles, which deviates from 90°, yields the correction factor for the angular calculation. To this end, the sine track and the cosine track must however be normalized to the value range +/−1. The normalizing of the sine track and the cosine track is however impeded by signal noise and eccentricities.
The American patent application US2013300337 shows a known motor controller.